RILEM TC 282-CCL: Calcined Clays as Supplementary Cementitious Materials

The most suitable path to achieve sustainability in cement production is the reduction of the clinker factor by adding Supplementary Cementitious Materials (SCM). The most common SCMs used today are fly ash, slag, and natural pozzolan. The reduction of steel production and phasing out of coal power plants has reflected in a significant decrease in the supply of these common SCMs, which represent less than 10% of the global cement production. The scarcity of common SCMs has prompted the use of calcined clays as an alternative. Calcined clays have been used for decades as pozzolans. Recent developments have shown that clays containing at least 40% of kaolinite as main clay mineral can be highly reactive if properly thermally activated. If limestone is added into the cement – calcined clay blend, the synergy between the two SCMs enables higher clinker substitution, with an improved performance both in terms of mechanical properties and durability. There is a growing number of research groups working on the subject of calcined clays in Europe, Asia and Latin America. Further, a significant amount of clays from around the world has been characterized. The integration of this work into pre-standards will pave the way for a wider usage of the material.